The Long Term Evolution (LTE) is a new terrestrial mobile communication standard currently being standardized by the 3GPP (3rd Generation Partnership Project). The Radio Access Network (RAN) of LTE is named as the Evolved-Universal Terrestrial Radio Access Network (E-UTRAN). The E-UTRAN physical layer is based on Orthogonal Frequency Division Multiplexing (OFDM). More precisely; the downlink transmission scheme is based on conventional OFDM using a cyclic prefix while the uplink transmission is based on single carrier frequency division multiple access (SC-FDMA) techniques. LTE supports both frequency division duplex (FDD) and time division duplex (TDD).
Data in terms of bits are transported from eNodeB to user equipment (UE) in the downlink direction and UE to eNodeB in the uplink direction. If we consider only uplink flow from UE to eNodeB then data is first received by Packet data convergence protocol (PDCP) layer and after performing compression and ciphering and/or integrity if applicable, will pass on the data to the Radio Link Control(RLC) Layer. Medium Access Control (MAC) will give the grant to the RLC layer for Radio Link Control Protocol Data Unit (RLC PDU) formation. RLC layer will concatenate or segment the data coming from PDCP layer into correct block size (block size will be given to RLC by MAC Scheduler in terms of grant) and forward RLC PDU to the MAC layer with its own header.
Now MAC layer selects the modulation and coding scheme and configures the physical layer. The data is now in the shape of transport block size and needed to be transmitted in 1 milli second (ms) subframe. Since the size of transport block is not fixed, the bit streams referred to as user Queue size will not be exactly equivalent to the possible transport block sizes given in 3GPP Technical Specification 36.213 V9.3 Table 7.1.7.2.1-1. Therefore to match the user data to the selected transport block size, zeroes will be appended to the user data. The transport block size which has less number of zero padding may require more resources for transmission. Therefore there is a need for determining appropriate transport block size to avoid more zero padding, to reduce overhead and increase throughput.